Do not allow header length to be zero in non-zero length packet

[radarhere]

Resolves #1524

Investigating the file attached to that issue, I found that at

openjpeg/src/lib/openjp2/t2.c

Line 1354 in e8b9d92

l_header_length = (OPJ_UINT32)(l_header_data - *l_header_data_start);

the header length was sometimes set to zero.

It seems intuitively not good for the header length to be zero in non-zero length packet, so I suggest returning OPJ_FALSE for that situation.

If this isn't a good solution, thanks for your time, and please let me know what I've missed.